1. Field of the Invention
This invention relates to articulable columns composed of segmented members held in a set position by friction created and maintained at the member interface by a tensioned means. In particular this invention relates to a method and means for building an improved column of this nature.
2. Description of Prior Art
Articulable columns have long been known for use in positioning micrometers and other measurement tools, or as electric light stands.
U.S. Pat. No. 599,543 discloses a support for incandescent electric lamps where the column is composed of a series of ball/socket members. An extension spring through the column provides tension to lock the column in place. Electrical wires run inside this spring from the base to the lamp fixture.
U.S. Pat. No. 870,429 discloses a sectional stand where a steel cable is used to maintain tension on the ball/socket members. Also a mechanism is provided to increase or decrease tension on the cable.
U.S. Pat. No. 912,308 discloses a sectional stand using alternating bend axis ball/socket members and a detachable means of removing the lamp fixture. Also disclosed is a spirally wound steel cable which forms the tensioned flexible cable. Electrical wires run inside this cable.
U.S. Pat. No. 936,379 discloses an adjustable lamp bracket in which the articulable column is composed of alternating ball and socket members.
U.S. Pat. No. 1,279,803 discloses a light support where a mechanism is provided to readily change tension on an extension spring to increase or decrease stiffness of the column.
U.S. Pat. No. 2,510,198 discloses the use of a flexible positioner as a tool holder. A means is provided to adjust the cable tension. A protective, flexible covering over the column is also shown.
U.S. Pat. No. 3,096,962 discloses a locking device for a measuring apparatus or the like where a single cam mechanism locks both the articulable column and the tool in place.
U.S. Pat. No. 3,529,797 discloses a supporting stand for instruments, primarily surgical instruments, in which the stand can be readily disassembled, sterilized, and reassembled. A wedge mechanism tensions the articulable column cable.
U.S. Pat. No. 3,584,822 discloses a flexible column where the column can be locked or unlocked with a lever at the free end. Electrical wires run alongside a steel tensioning cable inside the column. Means are provided to prevent the column from being twisted.
The disadvantage to prior art columns is that they are not adapted to accommodate the forces acting in the column. Consequently they tend to sag when extended out horizontally to the floor and they are difficult to adjust into new positions.
When an articulable column is held or positioned horizontally to the floor, a large bending moment exists at the base joint of the column from which the full weight of the column and its tool is cantilevered. At the free end, column joints see only a small bending moment due to the free end weight multiplied by a short moment arm. Prior art columns (e.g. 599,543, 936,379, 2,510,198, 3,096,962, 3,168,274, and 3,584,822) built with a stack of identical ball and socket members are not adapted to these varying forces. Because each joint is identical, the stiffness of each joint is the same and therefore under load these columns tend to sag at the base joint where the force is greatest. Adjustment of these columns by gripping the column at the free end is also difficult because, if partially locked, the column remains stiff at the free end while persistently bending at the weakest base joint, or if tension in the column is completely released, the column collapses.
Prior art columns in which the diameter of the ball/socket members is greater at the base than at the free end (e.g. 870,429, 912,308, and 1,279,803) acknowledge the varying forces acting in the column. However for long columns it is an unwieldy and inelegant method and difficult to manufacture.
Accordingly it is an object of this invention to provide an improved method of articulable column construction that overcomes the difficulties of column sag and adjustment.
To accomplish this it is an object of this invention to provide a method for controlling the stiffness at each joint in a segmented articulable column by controlling the friction at each joint interface. By controlling the stiffness of each joint with friction, articulable columns can be built which: (1) are stiff at the base joints where acting forces are large and (2) are relatively flexible at joints near the free end where acting forces are smaller. This allows columns to be built which are slender, articulable, structural members which can support large free end loads, and/or long column lengths. Columns built with this method also can be articulated in a natural, effective fashion.